1. Field of the Invention
This invention relates to a method for the recovery of useful metallic components, and more particularly to a method for the recovery of useful metallic components such as lead, tin, copper, etc. from a closely layered member having its surface layer of copper or a copper or aluminum alloy closely layered on a back metal such as a steel plate or the like.
2. Description of the Prior Art
Heretofore, a closely layered member having its surface layer of copper or a copper or aluminum alloy closely layered on a back metal such as a steel plate or the like has been employed for bearings of vehicles and the like. In such bearings, metallic components such as tin, lead, copper, etc. are added as alloying elements of the surface layer to provide for improved mechanical and chemical properties of the bearings and enhanced lubrication thereof.
The bearings are produced by stamping such a sheet-shaped, closely layered material into a predetermined shape. Therefore, in the fabrication of such bearings, many chips and scraps result from stamping and expensive metallic components such as lead, tin, copper, etc. are contained in the scraps. Since such chips and scraps contain large amounts of tin, copper, etc. as mentioned about, the recovery of these metallic components is usually carried out. However, a conventional method of recovery presents serious problems from the viewpoints of its equipment and health of laborers.
The chips and scraps are also layered members composed of a back metal as of steel and an aluminum alloy containing tin, copper, etc. and layered on the back metal, as is evident from the above. The back metal, that is, steel, is separated from the aluminum alloy and retained for later use. With a conventional method, lead is heated up to at least 926.degree. C., for example, in a crucible to provide a lead bath. Then, chips and scraps such as mentioned above are put in the lead bath, by which the copper alloy is dissolved, and then the back metal of steel, which is not dissolved in the lead bath, is taken out therefrom. Thus, the steel can be recovered with ease. On the other hand, the components of the copper alloy dissolved in the lead bath separate in layers due to the difference of their specific gravity. Namely, copper gathers in the upper part of the lead bath and lead and tin gather in the form of solid solution in the lower part. In such a case, however, the metallic components separated in layers cannot be recovered in the form of liquid, so that they are recovered in solid form after cooled, but the crucible must be broken for each recovery.
Further, since the melting point of lead is as high as 926.degree. C., lead evaporates during the recovery and, since the work is carried out under high-temperature condition, it is difficult and presents serious problems from the viewpoint of health of workers.
Moreover, a crucible of graphite is employed because of high temperature but even such a crucible is readily eroded by lead to introduce the possibilities such as blow-out of the liquid metal during the operation.